- Introduction
- Specification
- Examples
- Glossary
- Work in progress for future versions
The intent of this document is to outline the OpenSLO specification.
The goal of this project is to provide an open specification for defining SLOs to enable a common, vendor–agnostic approach to tracking and interfacing with SLOs. Platform-specific implementation details are purposefully excluded from the scope of this specification.
OpenSLO is an open specification i.e., it is a specification created and controlled, in an open and fair process, by an association or a standardization body intending to achieve interoperability and interchangeability. An open specification is not controlled by a single company or individual or by a group with discriminatory membership criteria. Additionally, this specification is designed to be extended where needed to meet the needs of the implementation.
Before making a contribute please read our contribution guideline.
- Compliance with the Kubernetes YAML format
- Vendor-agnostic
- Be flexible enough to be extended elsewhere
apiVersion: openslo/v1
kind: DataSource | SLO | SLI | AlertPolicy | AlertCondition | AlertNotificationTarget | Service
metadata:
name: string
displayName: string # optional
labels: # optional, it's allowed to assign multiple values to a single key
# example labels
organization: "acme"
team:
- "identity"
- "rbac"
costCentre: "project1"
serviceTier:
- "tier-1"
annotations: # optional
# example annotations
openslo.com/key1: value1
fooimplementation.com/key2: value2
spec:- kind string - required, one of: DataSource, SLO, SLI, AlertPolicy, AlertCondition, AlertNotificationTarget, Service
- metadata.name: string - required field
- all implementations must at least support object names that follow RFC1123:
- are up to 63 characters in length
- contain lowercase alphanumeric characters or
- - start with an alphanumeric character
- end with an alphanumeric character
- implementations are additionally encouraged to support names that:
- are up to 255 characters in length
- contain lowercase alphanumeric characters or
-,.,|,/,\
- all implementations must at least support object names that follow RFC1123:
- metadata.labels: map[string]string|string[] - optional field
key<>value- the
keysegment is required and must contain at most 63 characters beginning and ending with an alphanumeric character[a-z0-9A-Z]with dashes-, underscores_, dots.and alphanumerics between. - the
valueofkeysegment can be a string or an array of strings
- the
- metadata.annotations: map[string]string - optional field
key<>valueannotationsshould be used to define implementation / system specific metadata about the SLO. For example, it can be metadata about a dashboard url, or how to name a metric created by the SLI, etc.keyhave two segments: an optionalprefixandname, separated by a slash/- the
namesegment is required and must contain at most 63 characters beginning and ending with an alphanumeric character[a-z0-9A-Z]with dashes-, underscores_, dots.and alphanumerics between. - the
prefixis optional and must be a DNS subdomain: a series of DNS labels separated by dots., it must contain at most 253 characters, followed by a slash/. - the
openslo.com/is reserved for OpenSLO usage
The duration shorthand is specified as a single–word string (no whitespaces) consisting
of a positive integer number followed by a case–sensitive single–character postfix.
Allowed postfixes are:
- m – minutes
- h – hours
- d – days
- w – weeks
- M – months
- Q – quarters
- Y – years
Examples: 12h, 4w, 1M, 1Q, 365d, 1Y.
This specification does not put requirements on how (or whether) to implement each postfix, therefore implementers are free to pick an implementation that best suits their environments.
There is however the possibility that future versions of this spec will take a more prescriptive stance on this issue.
💡 Note: Specific attributes are described in detail in the Notes subsection of each object type's section.
A DataSource represents connection details with a particular metric source.
apiVersion: openslo/v1
kind: DataSource
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
type: string # predefined type e.g. Prometheus, Datadog, etc.
connectionDetails:
# fields used for creating a connection with particular datasource e.g. AccessKeys, SecretKeys, etc.
# everything that is valid YAML can be put hereDataSource enables reusing one source between many SLOs and moving connection specific details (e.g. authentication) away from SLO definitions.
This spec does not enforce naming conventions for data source types, however the OpenSLO project will publish guidelines in the form of supplementary materials once common patterns start emerging from implementations.
An example of the DataSource kind can be:
apiVersion: openslo/v1
kind: DataSource
metadata:
name: string
displayName: string # optional
spec:
type: CloudWatch
connectionDetails:
accessKeyID: accessKey
secretAccessKey: secretAccessKeyA service level objective (SLO) is a target value or a range of values for a service level that is described by a service level indicator (SLI).
apiVersion: openslo/v1
kind: SLO
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
service: string # name of the service to associate this SLO with, may refer (depends on implementation) to existing object Kind: Service
indicator: # see SLI below for details
indicatorRef: string # name of the SLI. Required if indicator is not given.
timeWindow:
# exactly one item; one of possible: rolling or calendar–aligned time window
## rolling time window
- duration: duration-shorthand # duration of the window eg 1d, 4w
isRolling: true
# or
## calendar–aligned time window
- duration: duration-shorthand # duration of the window eg 1M, 1Q, 1Y
calendar:
startTime: 2020-01-21 12:30:00 # date with time in 24h format, format without time zone
timeZone: America/New_York # name as in IANA Time Zone Database
isRolling: false # if omitted assumed `false` if `calendar:` is present
budgetingMethod: Occurrences | Timeslices | RatioTimeslices
objectives: # see objectives below for details
alertPolicies: # see alert policies below for details-
indicator optional, represents the Service Level Indicator (SLI), described in SLI section. One of
indicatororindicatorRefmust be given. If declaring composite SLO must be moved intoobjectives[]. -
indicatorRef optional, this is the name of Service Level Indicator (SLI). One of
indicatororindicatorRefmust be given. If declaring composite SLO must be moved intoobjectives[]. -
timeWindow[ ] optional, TimeWindow is a list but accepting only exactly one item, one of the rolling or calendar aligned time window:
- Rolling time window. Duration should be provided in shorthand format e.g. 5m, 4w, 31d.
- Calendar Aligned time window. Duration should be provided in shorthand format eg. 1d, 2M, 1Q, 366d.
-
description string optional field, contains at most 1050 characters
-
budgetingMethod enum(Occurrences | Timeslices | RatioTimeslices), required field
- Occurrences method uses a ratio of counts of good events to the total count of the events.
- Timeslices method uses a ratio of good time slices to total time slices in a budgeting period.
- RatioTimeslices method uses an average of all time slices' success ratios in a budgeting period.
-
objectives[ ] Threshold, required field, described in Objectives section. If
thresholdMetrichas been defined, only one Threshold can be defined. However, if usingratioMetricthen any number of Thresholds can be defined. -
alertPolicies[ ] AlertPolicy, optional field. section. An alert policy can be defined inline or can refer to an Alert Policies object, in which case the following are required:
- alertPolicyRef string: this is the name or path to the AlertPolicy
Objectives are the thresholds for your SLOs. You can use objectives to define the tolerance levels for your metrics.
objectives:
- displayName: string # optional
op: lte | gte | lt | gt # conditional operator used to compare the SLI against the value. Only needed when using a thresholdMetric
value: numeric # optional, value used to compare threshold metrics. Only needed when using a thresholdMetric
target: numeric [0.0, 1.0) # budget target for given objective of the SLO, can't be used with targetPercent
targetPercent: numeric [0.0, 100) # budget target for given objective of the SLO, can't be used with target
timeSliceTarget: numeric (0.0, 1.0] # required only when budgetingMethod is set to TimeSlices
timeSliceWindow: number | duration-shorthand # required only when budgetingMethod is set to TimeSlices or RatioTimeslices
indicator: # required only when creating composite SLO, see SLI below for more details
indicatorRef: string # required only when creating composite SLO, required if indicator is not given.
compositeWeight: numeric (0.0, inf+] # optional, supported only when declaring multiple objectives, default value 1.Example:
objectives:
- displayName: Foo Total Errors
target: 0.98
- displayName: Bar Total Errors
targetPercent: 99.99-
op enum( lte | gte | lt | gt ), operator used to compare the SLI against the value. Only needed when using a
thresholdMetric -
value numeric, required field, used to compare values gathered from metric source. Only needed when using a
thresholdMetric.
Either target or targetPercent must be used.
-
target numeric [0.0, 1.0), optional, but either this or
targetPercentmust be used. Budget target for a given objective of the SLO. Atarget: 0.9995is equivalent totargetPercent: 99.95. -
targetPercent: numeric [0.0, 100), optional, but either this or
targetmust be used. Budget target for a given objective of the SLO. AtargetPercent: 99.95is equivalent totarget: 0.9995. -
timeSliceTarget numeric [0.0, 1.0], required only when budgeting method is set to TimeSlices
-
timeSliceWindow (numeric | duration-shorthand), required only when budgeting method is set to TimeSlices or RatioTimeslices. Denotes the size of a time slice for which data will be evaluated e.g. 5, 1m, 10m, 2h, 1d. Also ascertains the frequency at which to run the queries. Default interpretation of unit if specified as a number in minutes.
-
indicator optional, represents the Service Level Indicator (SLI), described in SLI section. One of
indicatororindicatorRefmust be given in objective when creating composite SLO. -
indicatorRef optional, this is the name of Service Level Indicator (SLI). One of
indicatororindicatorRefmust be given when creating composite SLO.
Composite SLO goal of composite SLO is to enable user an end-to-end journey, it is done by defining many independent objectives. Each objective can have different queries, data sources and targets. The basic implementation assumes that the Composite Error Budget burns if the Error Budget for any of the SLO objectives within the Composite SLO is burning. The logic of those calculations is the same for Composite SLOs as for regular (standard) objectives and SLOs.
Weight allows the user to change the impact of a given SLO on the whole composite SLO. Weight is just multiplier, it
means that if weight is 0.5, SLO will have half impact as default, on the other hand if weight is 100, this SLO will
be 100 times more impactful. By default, weight has value 1 and doesn't need to be specified.
Calculations should be as simple as possible to make composite SLO intuitive and easy to implement. It is hard to compare different error budget calculating methods therefore all composite objectives need to be calculated with one type of error budget calculating method. Here is brief description how given budgeting method should impact composite SLO and how wight scale its impact:
- Occurrences - if SLO burns its budget composite is burning its budget at the same rate. Each violation that consumed SLO's budget will impact Composite at the same rate. Weight multiplies the rate of burning of SLO (referenced as burn rate) that burns composite.
- Timeslices - this is binary depending on whether it was a good or bad minute. If it was a bad minute for any individual objective, it's considered a bad minute for the Composite SLO.
- Ratiotimeslices - it is the sum of missing up to 100 percent. If two SLOs have average of Ratiotimeslices on 95%, composite will have average of Ratiotimeslices on 90%. Weight multiplies missing part of given slo.
A service level indicator (SLI) represents how to read metrics from data sources.
apiVersion: openslo/v1
kind: SLI
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
thresholdMetric: # either thresholdMetric or ratioMetric must be provided
metricSource:
metricSourceRef: string # optional, this field can be used to refer to DataSource object
type: string # optional, this field describes predefined metric source type e.g. Prometheus, Datadog, etc.
spec:
# arbitrary chosen fields for every data source type to make it comfortable to use
# anything that is valid YAML can be put here.
ratioMetric: # either thresholdMetric or ratioMetric must be provided
counter: true | false # true if the metric is a monotonically increasing counter,
# or false, if it is a single number that can arbitrarily go up or down
# ignored when using "raw"
good: # the numerator, either "good" or "bad" must be provided if "total" is used
metricSource:
metricSourceRef: string # optional
type: string # optional
spec:
# arbitrary chosen fields for every data source type to make it comfortable to use.
bad: # the numerator, either "good" or "bad" must be provided if "total" is used
metricSource:
metricSourceRef: string # optional
type: string # optional
spec:
# arbitrary chosen fields for every data source type to make it comfortable to use.
total: # the denominator used with either "good" or "bad", either this or "raw" must be used
metricSource:
metricSourceRef: string # optional
type: string # optional
spec:
# arbitrary chosen fields for every data source type to make it comfortable to use.
rawType: success | failure # required with "raw", indicates how the stored ratio was calculated:
# success – good/total
# failure – bad/total
raw: # the precomputed ratio stored as a metric, can't be used together with good/bad/total
metricSource:
metricSourceRef: string # optional
type: string # optional
spec:
# arbitrary chosen fields for every data source type to make it comfortable to use.- description string optional field, contains at most 1050 characters
Either ratioMetric or thresholdMetric must be used.
-
thresholdMetric Metric, represents the query used for gathering data from metric sources. Raw data is used to compare objectives (threshold) values.
-
ratioMetric Metric {good, total}, {bad, total} or raw.
-
counter enum(true | false), specifies whether the metric is a monotonically increasing counter. Has no effect when using a
rawquery. -
good represents the query used for gathering data from metric sources used as the numerator. Received data is used to compare objectives (threshold) values to find good values. If
badis defined thengoodmust not be set. -
bad represents the query used for gathering data from metric sources used as the numerator. Received data is used to compare objectives (threshold) values to find bad values. If
goodis defined thenbadmust not be set. -
total represents the query used for gathering data from metric sources that is used as the denominator. Received data is used to compare objectives (threshold) values to find total number of metrics.
-
rawType enum(success | failure), required when using
raw, specifies whether the ratios represented by the "raw" ratio metric are of successes or failures. Not to be used withgoodandbadas picking one of those determines the type of ratio. -
raw represents the query used for gathering already precomputed ratios. The type of ratio (success or failure) is specified using
rawType.
-
An example of an SLO where SLI is inlined:
apiVersion: openslo/v1
kind: SLO
metadata:
name: foo-slo
displayName: Foo SLO
spec:
service: foo
indicator:
metadata:
name: foo-error
displayName: Foo Error
spec:
ratioMetric:
counter: true
good:
metricSource:
metricSourceRef: datadog-datasource
type: Datadog
spec:
query: sum:trace.http.request.hits.by_http_status{http.status_code:200}.as_count()
total:
metricSource:
metricSourceRef: datadog-datasource
type: Datadog
spec:
query: sum:trace.http.request.hits.by_http_status{*}.as_count()
objectives:
- displayName: Foo Total Errors
target: 0.98If a service level indicator has ratioMetric defined, the following maths can
be used to calculate the value of the SLI. Below we describe the advised formulas
for calculating the indicator value.
Good-Total queries
If the good and total queries are given then following formula can be used
to calculate the value:
indicatorValue = good / total
If we have 99 good requests out of a total of 100 requests, the calculated value
for the indicator would be: 99 / 100 = 0.99. This represents 99% on a 0-100 scale
using the formula 0.99 * 100 = 99.
Bad-Total queries
If the bad and total queries are given then following formula can be used
to calculate the value:
indicatorValue = ( total - bad ) / total
If we have 1 error out of a total of 100 requests, the calculated value for
the indicator would be: (100 - 1) = 0.99. This represents 99% on a 0-100 scale
using the formula 0.99 * 100 = 99.
💡 Note: As you can see for both query combinations we end up with the same calculated value for the service level indicator.
The required spec key will be used to pass extraneous data to the data source. The goal of this approach
is to provide maximum flexibility when querying data from a particular source. In the following examples
we can see that this works fine for both simple and more complex cases.
An example of ratioMetric:
ratioMetric:
counter: true
good:
metricSource:
type: Prometheus
metricSourceRef: prometheus-datasource
spec:
query: sum(localhost_server_requests{code=~"2xx|3xx",host="*",instance="127.0.0.1:9090"})
total:
metricSource:
type: Prometheus
metricSourceRef: prometheus-datasource
spec:
query: localhost_server_requests{code="total",host="*",instance="127.0.0.1:9090"}An example of thresholdMetric:
thresholdMetric:
metricSource:
metricSourceRef: redshift-datasource
spec:
region: eu-central-1
clusterId: metrics-cluster
databaseName: metrics-db
query: SELECT value, timestamp FROM metrics WHERE timestamp BETWEEN :date_from AND :date_toField type can be omitted because the type will be inferred from the DataSource when metricSourceRef is specified.
An example thresholdMetric that does not reference a defined DataSource:
thresholdMetric:
metricSource:
type: Redshift
spec:
region: eu-central-1
clusterId: metrics-cluster
databaseName: metrics-db
query: SELECT value, timestamp FROM metrics WHERE timestamp BETWEEN :date_from AND :date_to
accessKeyID: accessKey
secretAccessKey: secretAccessKeyField type can't be omitted because the reference to an existing DataSource is not specified.
An Alert Policy allows you to define the alert conditions for an SLO.
apiVersion: openslo/v1
kind: AlertPolicy
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
alertWhenNoData: boolean
alertWhenResolved: boolean
alertWhenBreaching: boolean
conditions: # list of alert conditions
- conditionRef: # required when alert condition is not inlined
notificationTargets:
- targetRef: # required when alert notification target is not inlined- description string, optional description about the alert policy, contains at most 1050 characters
- alertWhenBreaching boolean,
true,false, whether the alert should be triggered when the condition is breaching - alertWhenResolved boolean,
true,false, whether the alert should be triggered when the condition is resolved - alertWhenNoData boolean,
true,false, whether the alert should be triggered when the condition indicates that no data is available - conditions[ ] Alert Condition, an array, (max of one condition), required field.
A condition can be defined inline or can refer to external Alert condition defined in this case the following are required:
- conditionRef string: this is the name or path the Alert condition
- notificationTargets[ ] Alert Notification Target, required field.
A condition can be defined inline or can refer to an AlertNotificationTarget
object, in which case the following are required:
- targetRef string: this is the name or path to the AlertNotificationTarget
💡 Note: The
conditionsfield is of the typearrayof AlertCondition but only allows one single condition to be defined. The use of an array is for future-proofing purposes.
An example of an Alert policy which refers to another Alert Condition:
apiVersion: openslo/v1
kind: AlertPolicy
metadata:
name: AlertPolicy
displayName: Alert Policy
spec:
description: Alert policy for cpu usage breaches, notifies on-call devops via email
alertWhenBreaching: true
alertWhenResolved: false
conditions:
- conditionRef: cpu-usage-breach
notificationTargets:
- targetRef: OnCallDevopsMailNotificationAn example of an Alert Policy were the Alert Condition is inlined:
apiVersion: openslo/v1
kind: AlertPolicy
metadata:
name: AlertPolicy
displayName: Alert Policy
spec:
description: Alert policy for cpu usage breaches, notifies on-call devops via email
alertWhenBreaching: true
alertWhenResolved: false
conditions:
- kind: AlertCondition
metadata:
name: cpu-usage-breach
displayName: CPU Usage breaching
spec:
description: SLO burn rate for cpu-usage-breach exceeds 2
severity: page
condition:
kind: burnrate
op: lte
threshold: 2
lookbackWindow: 1h
alertAfter: 5m
notificationTargets:
- targetRef: OnCallDevopsMailNotificationAn Alert Condition allows you to define under which conditions an alert for an SLO needs to be triggered.
apiVersion: openslo/v1
kind: AlertCondition
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
severity: string # required
condition: # required
kind: string
op: enum
threshold: number
lookbackWindow: duration-shorthand
alertAfter: duration-shorthand- description string, optional description about the alert condition, contains at most 1050 characters
- severity string, required field describing the severity level of the alert (ex. "sev1", "page", etc.)
- condition, required field. Defines the conditions of the alert
- kind enum(burnrate) the kind of alerting condition thats checked, defaults to
burnrate
- kind enum(burnrate) the kind of alerting condition thats checked, defaults to
If the kind is burnrate the following fields are required:
- op enum(lte | gte | lt | gt), required field, the conditional operator used to compare against the threshold
- threshold number, required field, the threshold that you want alert on
- lookbackWindow duration-shorthand, required field, the time-frame for which to calculate the threshold e.g.
5m - alertAfter duration-shorthand: required field, the duration the condition needs to be valid for before alerting, defaults to
0m
If the alert condition is breaching, and the alert policy has alertWhenBreaching set to true
the alert will be triggered
If the alert condition is resolved, and the alert policy has alertWhenResolved set to true
the alert will be triggered
If the service level objective associated with the alert condition returns
no value for the burn rate, for example, due to the service level indicators
missing data (e.g. no time series being returned) and the alertWhenNoData
is set to true the alert will be triggered.
💡 Note: The
alertWhenBreachingandalertWhenResolved,alertWhenNoDatacan be combined, if you want an alert to trigger whenever at least one of these conditions is true.
An example of an alert condition:
apiVersion: openslo/v1
kind: AlertCondition
metadata:
name: cpu-usage-breach
displayName: CPU usage breach
spec:
description: If the CPU usage is too high for given period then it should alert
severity: page
condition:
kind: burnrate
op: lte
threshold: 2
lookbackWindow: 1h
alertAfter: 5mAn Alert Notification Target defines the possible targets where alert notifications should be delivered to. For example, this can be a web-hook, Slack or any other custom target.
apiVersion: openslo/v1
kind: AlertNotificationTarget
metadata:
name: string
displayName: string # optional, human readable name
spec:
target: # required
description: # optionalAn example Alert Notification Target:
apiVersion: openslo/v1
kind: AlertNotificationTarget
metadata:
name: OnCallDevopsMailNotification
spec:
description: Notifies by a mail message to the on-call devops mailing group
target: emailAlternatively, a similar notification target can be defined for Slack like this:
apiVersion: openslo/v1
kind: AlertNotificationTarget
metadata:
name: OnCallDevopsSlackNotification
spec:
description: "Sends P1 alert notifications to the slack channel"
target: slack- target string, describes the target of the notification, e.g. Slack, email, web-hook, Opsgenie etc
- description string, optional description about the notification target, contains at most 1050 characters
💡 Note: The way the alert notification targets are is an implementation detail of the system that consumes the OpenSLO specification.
For example, if the OpenSLO is consumed by a solution that generates Prometheus recording rules, and alerts, you can imagine that the name of the alert notification gets passed as a label to Alertmanager which then can be routed accordingly based on this label.
A Service is a high-level grouping of SLO. It may be defined before creating SLO to be able to refer to it in SLO's spec.service.
Multiple SLOs can refer to the same Service.
apiVersion: openslo/v1
kind: Service
metadata:
name: string
displayName: string # optional
spec:
description: string # optional up to 1050 characters
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